2 commonly used terms in MPLS are LDP and RSVP-TE. While the former relates to easy provisioning in MPLS setup, the latter i.e. RSVP-TE is related to guarantee bandwidth for traffic communication.
LDP setups LSPs based on routing data, whereas RSVP setups additional traffic engineered LSPs.
LDP is an abbreviation for Label Distribution Protocol that defines a set of process and messages by which one LSR (Label Switched Router) informs another of the label bindings. LSR further establishes label switched paths through a network by mapping network-layer routing information to data-link layer path.
In the case of MPLS LDP, Label bindings are established automatically for specific FECs (behaviour is different by different vendors).
RSVP-TE is used to establish MPLS transport LSPs for meeting traffic engineering requirements. It is mainly used to provide QoS and load balancing across the network including optical Core network.
The RSVP-TE (traffic extension) protocol is an addition to the RSVP protocol with extensions to allow it to set up optical paths in an agile optical network.
RSVP is the primary choice if we need to perform Traffic Engineering ie FRR, DiffServ-TE, Explicit Routing etc.
LDP vs RSVP
Below table differentiates between MPLS LDP and RSVP(-TE) –
| PARAMETER | LDP | RSVP |
|---|---|---|
| Abbreviation for | Label Distribution protocol | Resource Reservation Protocol |
| Provisioning | Easy to configure. We just need to enable on interfaces. Label bindings automatically established for specific FECs | Complex configuration |
| Topology | LSPs from multiple ingresses use the same label to reach the egress (multi-point to point LSP) | RSVP sets up independent point to point LSPs. |
| QoS | Limited | Guaranteed resources |
| LSP setup initiation | Egress initiates the LSP setup | Ingress initiates the LSP setup. |
| Requirement | If primarily LSPs need to be set up, LDP should be used | If you require traffic engineering and resources reservations, use RSVP (-TE). |
| Scalability | High | Low |
| ECMP | Possible | Not Possible |
| Fast Reroute (FRR) support | No | Yes |
| IGP based decision making | LDP follows IGP for decision making | RSVP does not follow the IGP, and take independent decisions on the reserved traffic |
Download the difference table here.
Related – MPLS vs IP Routing
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